Internal combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines exhaust a complex mixture of air pollutants as byproducts of the combustion process. These air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of NOx emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions has been to implement exhaust gas regeneration (EGR). EGR systems recirculate exhaust gas to mix with combustion air supplied to an engine. The recirculated exhaust gas reduces a concentration of oxygen and increases a thermal mass within the engine's cylinders, thereby lowering a resulting combustion temperature. The lowered combustion temperature slows the chemical reaction of the combustion process and decreases the formation of NOx.
Although successful at reducing NOx, the effectiveness of an EGR system can vary based on an ability to mix the recirculated exhaust with air prior to the mixture being received and combusted within the engine's cylinders. That is, when the recirculated exhaust is thoroughly mixed with combustion air, each cylinder receiving that mixture produces sufficient power and emits exhaust with a low NOx concentration. However, if the exhaust is poorly mixed with the combustion air, some cylinders may receive a mixture having a high concentration of exhaust and correspondingly produce little power, while other cylinders may receive a mixture having a low concentration of exhaust and correspondingly produce excessive amounts of NOx. This situation can be exacerbated when fewer than all of the engine's cylinders contribute exhaust for the recirculation process, as the resulting pulses of recirculated exhaust from the contributing cylinders are not equally distributed during the ensuing intake strokes of the engine.
U.S. Pat. No. 6,237,336 to Feucht et al. (“the '336 patent”) discloses an EGR system that attempts to improve the distribution and mixing of recirculated exhaust with combustion air. Specifically, the '336 patent describes a six-cylinder, turbocharged engine having an exhaust manifold connected to three of the engine's cylinders, and an intake manifold providing combustion air to all of the cylinders. The EGR system includes a mixing vessel having two inlets, an outlet, and a mixing chamber. A first of the inlets is fluidly connected to the exhaust manifold, while a second of the inlets is fluidly connected to a turbocharger. The outlet is fluidly connected with the intake manifold.
A volume of the mixing vessel of the '336 patent is set equal to the displacement volume of two cylinders. The first inlet extends alongside the vessel and includes two discharge openings into the vessel, which are spaced apart along a length of the inlet by the volume of one cylinder displacement. In this manner, exhaust pulses received from each of the three contributing cylinders may be used to create two discharge pulses of exhaust into the mixing vessel (six total pulses per cycle) that are separated by the volume of one cylinder displacement such that the recirculated exhaust gas is evenly distributed and received by the six cylinders of the engine during the ensuing intake strokes.
Although the system in the '336 patent may be an improvement over prior systems, it may still be less than optimal. Specifically, because the discharge openings extend along a length of the inlet, the flows of exhaust from the exhaust manifold into the vessel may not be true parallel flows. As a result, downstream openings may discharge exhaust at a lower pressure and flow rate than upstream openings, and the exhaust pulses discharged into the flow of combustion air could be inconsistent. In some applications, inconsistent exhaust pulses could cause performance of the engine to be less than desired.
The disclosed exhaust gas recirculation system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.